Oh, sorry... I was being brain dead the first time I replied.
You also need to specify what is being removed, ie 'clearpart --all
--drives=hda' to remove all partitions from hda. Otherwise, it still defaults
to not removing any types of partitions.

'clearpart --all --drives sda' delete all partitions on both sda and sdb
and stopped at 'part /backup --size 4096 --onpart sdb1 --noformat --grow'.
How can I delete all partitions on hda and reallocate sdb1?